The most deadly virus on earth.

In the 1970s, Europe experienced an unusual phenomenon when thousands of Chickenheads fell from the sky, creating a state of both confusion and joy among foxes and other wildlife. The reason behind this peculiar event was a concerted effort to combat a rampant rabies epidemic that had plagued wildlife populations in Europe since the 1930s. Humans sought to eliminate the deadliest virus known to humanity, and the Chickenheads served as carriers of a vaccine. Rabies, named after Lyssa, the ancient Greek spirit of mad rage, has haunted humanity for over 4000 years. Its effects are both bizarre and lethal, turning animals into aggressive beasts and humans into water-fearing zombies.

What makes Lyssa particularly intriguing is not only the peculiar and deadly nature of its infection but also its remarkable ability to evade our immune defenses. Viruses, existing on the boundary between life and death, rely on living cells to replicate, with mere genetic instructions guiding their existence. The lyssavirus, a relatively simple virus, possesses only five genes, instructing the production of proteins crucial for infecting mammals, evading the immune system, reaching the brain, replicating, and infecting new hosts.

Upon infection, typically initiated by a bite, often from a virus-carrying dog, Lyssa infiltrates nerve cells, targeting neurons responsible for transmitting signals throughout the body. The virus capitalizes on the intricate structure of neurons, exploiting microtubules and dynein motors to travel along these cellular highways toward the nucleus, where it takes over the cell and produces more viruses.

While the immune system is our primary line of defense against viral infections, Lyssa manages to elude it effectively. Interferons, the proteins crucial for activating the immune response, are usually released by infected cells, alerting the immune system and inhibiting viral replication. Interferons also enhance cellular transparency, allowing immune cells to detect infections. However, Lyssa thwarts these defenses by blocking interferon production in neurons, rendering itself virtually invisible to the immune system.

Diverging from the conventional behavior of many viruses, Lyssavirus distinguishes itself by ensuring host survival during its replication process, avoiding triggering immediate alarm systems. Instead of swiftly annihilating its host, Lyssa discreetly navigates from neuron to neuron, embarking on a gradual journey towards the brain. This progression, spanning weeks to months and occasionally even years, is contingent upon variables such as the location of the bite (whether on the face or foot) and the quantity of viruses infiltrating the muscles. Demonstrating remarkable patience, Lyssa persists until it reaches its ultimate destination: the brainstem.

Upon this incursion into the brain, the immune system belatedly recognizes the intrusion and deploys its formidable antivirus cells, the Killer T Cells. Ordinarily, this mobilization would mark a turning point in viral infections; however, in the case of rabies, the T cells unwittingly rush toward their demise. Employing a mere five proteins, Lyssa executes a strategic maneuver akin to a reverse card in the game of Uno, turning the immune system's ingenuity against itself.

The central nervous system, a delicate component of the body, necessitates careful immune regulation. To prevent inadvertent damage, immune cells require an invitation to enter the nervous system and can be expelled if necessary. Lyssa manipulates infected neurons to express self-destruct orders, causing incoming T Cells, the immune system's powerhouse, to commit suicide. This maneuver facilitates the virus's infiltration of the brainstem, heralding an inevitable demise once this critical stage is reached.

Unveiling the enigma of Lyssavirus-induced mortality poses a challenge. Unlike traditional viral mechanisms that involve rapid multiplication and subsequent cell destruction, Lyssa's impact on the brain appears subtle. Autopsies of rabies patients reveal minimal or non-existent damage to brain tissue. The prevailing hypothesis suggests that Lyssa disrupts neural communication, incapacitating normal brain function and giving rise to symptoms like confusion, aggression, and paralysis.

As the virus progresses, it embarks on an intriguing journey, departing from the brain and traversing neurons en route to the salivary glands. The mechanism behind this reversal remains an enigma, even after decades of study. Lyssa saturates saliva, setting the stage for transmission through bites, initiating a cyclical pattern. Although this scenario might evoke images of a potential zombie outbreak, human-to-human rabies transmission via bites remains undocumented.

In the final stages, the afflicted individual experiences the rapid onset of encephalitis, characterized by brain swelling and a spectrum of neurological symptoms, from lethargy to paralysis. Organ failure ensues, culminating in a coma. Despite extensive research, there is no established therapy, and survival post-symptom onset is exceedingly rare. Lyssa stands as one of the deadliest viruses known to humanity, claiming approximately 60,000 lives annually, with children comprising nearly half of the victims.

However, there exists a beacon of hope against this formidable foe—the rabies vaccine. Among the earliest vaccines developed by humans, it equips the immune system to mount a swift defense against future Lyssavirus attacks. The vaccine's unique feature lies in its effectiveness even after exposure, as the slow progression of Lyssa allows for post-bite vaccinations. This becomes crucial, especially when individuals unknowingly encounter a bite from a seemingly inconspicuous carrier, such as a bat.

Rabies remains a lingering menace, echoing through the annals of human history, instilling fear in our ancestors, and persisting as a contemporary threat, claiming thousands of lives annually. Eradicating this malevolent force requires perpetual vigilance, as it lurks in the shadows, poised to resurge if humanity falters in its defense or succumbs to vaccine skepticism. The aspiration is for humanity to triumph over this monstrous adversary, relegating it to the realm of imagination like many legendary monsters. While the complexities of rabies extend beyond this brief exploration, delving into scientific sources can be daunting.